Clean up the area you want it to be. Use Liquid Nail or some bonding agent to bond the bricks to the ground. That alone is enough that my homies of 180lbs could skate and not have them budge until someone sledgehammers them. You lay the cinder blocks with the holes aligned vertically and then fill that with anything but for more strength some crete or mortor mix. To make it even stronger you could drill holes in the ground and have rebar in there. But I've done several ledges with just liquid nail and blocks and angle iron and that shit all lasted again until the unstoked property owners sledge that shit.